A traffic collision avoidance system (TCAS) is an aircraft collision avoidance system designed to reduce the incidence of mid-air collisions between aircraft. TCAS monitors the airspace around an aircraft for other aircraft equipped with a corresponding active transponder, independent of air traffic control, and warns pilots of the presence of other transponder-equipped aircraft which may present a threat of mid-air collision.
The antennas used by TCAS may include a directional antenna mounted on the top of the aircraft and a directional or omnidirectional antenna on the bottom of the aircraft. This antenna may enable a transponder to receive interrogations at 1030 MHz and reply to the received interrogations at 1090 MHz.
Because TCAS antennas are attached to the exterior surface of an aircraft, drag created by the antenna is a serious concern. TCAS antennas must, therefore, be as streamlined and low-profile as possible. Traditional TCAS antennas employ a low-profile radome configuration. The radome configuration offers a low-profile but generally operates over a very narrow band of approximately 1030 MHz to 1090 MHz; adequate for TCAS only.
In addition to TCAS, aircraft generally include other L-band radios. Because TCAS antennas generally operate in a very narrow band, such antennas are not suitable for use by other L band radios operating outside that narrow band. Aircraft must therefore incorporate additional antennas. Additional antennas and associated cables may cause additional drag, consume power, add weight and add cost.
Consequently, it would be advantageous if an apparatus existed that is suitable for use as a low-drag TCAS antenna, and for integrating various L-band radios in an aircraft.